One of the problems to be overcome in a coil of this kind lies in the way in which it is secured to the vehicle. The coil, which serves spark plugs corresponding in number to the number of cylinders in the engine, comprises at least two complete magnetic assemblies housed in a common casing. In consequence, its weight is not insignificant, being due in particular to the primary magnetic cores and to the magnetic flux return circuits which are constituted by a stack of stampled out magnetic laminations.
The anchorage for such an assembly must therefore be particularly effective and solid, so as to be able to resist all the forces to which the coil is subjected in a vehicle. One such anchorage, described in U.S. Pat. No. 4,763,094, involves forming, in the magnetic flux return circuit, holes in which the securing screws, for securing the coil to the vehicle, are engaged. This system does however have a number of disadvantages. Firstly, it necessitates machining of the magnetic flux return circuit, and admission of free air to part of the latter, which inevitably leads to its oxidation. Secondly, such an anchorage, since it forms an integral part of the metallic armature of the coil, has no flexibility which would enable it to absorb the substantial vibrations to which such an assembly is inevitably subjected in a vehicle during operation. This leads to a substantial risk of fracture of the securing screws.